Help With Figuring Out An Icing Recipe I Lost

I used to work at a bakery years ago where they had a simple icing recipe for their wedding cakes. I wrote it down back then, and thought I held on to the recipe, but I can't find it anywhere. I was hoping someone had one similar they could share. Unfortunately all I remember is that it had shortening (I don't think they used butter with it) and very hot water. I can't remember if they used powdered sugar or granulated sugar.

I just remember it being very light and airy. It looked like it was whipped cream, but when you tasted it, you could definitely tell it was more of a shortening based icing. They were able to ice it and make it look like fondant, very smooth with no spatula marks. It didn't crust at all.

I love the taste of my current buttercream recipe, and for the most part I can get mine to look very smooth, but was really looking to try theirs and am so frustrated I can't find it! Any thoughts would be helpful! Thank you!